After becoming infected by the mysterious and pandemic Medusa virus, Kasumi and her twin sister Shizuku are separated when only Kasumi is chosen to be one of a select group of 160 people to be placed in cyrogenic suspension until a cure can be found. After an undetermined amount of time in cold sleep, Kasumi eventually awakens along with a handful of others in now desolate and treacherous ruins populated by vicious creatures. While Kasumi may hope to learn the fate of her twin sister, they all hope to unravel much larger mysteries and must continue to survive after already sleeping through what may have been the apocalypse.